For the purpose of the present invention, the term “package unit” may also refer to an object, product or item which is not packed in a box or a case nor wrapped in paper as long as the product or item can be marked in such a way that the marking can not be removed without destruction or damaging of the said object. Likewise, a package unit such as a box or case is preferably packed in a way that it cannot be opened to take out the object or product packed therein without destruction or damaging of the said box or case. Whenever reference is made to a box in the present patent application, this shall also include other means of packaging such as cases, or wrappings.
A prerequisite for identification of objects and products is individually marking the objects and products themselves, or their packaging, i.e. boxes. Marking may be made by applying labels to the package unit, or by directly applying the marking to the package unit. A commonly used method is applying bar or dot codes.
Such bar codes may preferably be printed on the box or individual package unit with a device and process fully described in copending European Patent Application 04 009 792.5 which involves generating a combined hash code both from the pixel information sent to the printer, and from the printer-specific information which is collected during the printing operation, the combined information being converted to a hash code by a real time hash engine, i.e. during the process of printing itself. This process make it possible to print the hash code generated during printing of a page at the bottom of that very page. This hash code is preferably printed in the form of a bar code, or a dot pattern which is optically readable. Due to the fact that the hash code is calculated from the pixel information and the printer-specific data, it is comparable to a fingerprint which is unique for any combination of pixel information to be printed, and the specific printer used in the printing process. Any label or any print including this hash code is therefore unique.
Printer-specific information comprises, without limitation, counting the number of revolutions of the light-sensitive drum in a laser printer, irregularities of the rotation of such drum, movement of the mirror in a laser printer, rotation of rubber rolls involved in paper transport, and the movement of printing heads in ink-jet printers, as well as any data generated from the electronic circuitry which drives the printer.
It has also been known that RFID (radio frequency identification) tags may be used to identify products or objects. RFID tags are still expensive, and they also need expensive electronic circuitry to analyse the information within an RFID tag. An advantage of these RFID tags, however, is that they can be read from a distance, i.e. without direct visible contact, and that the amount of information stored may be considerably higher than that of a bar code. On the other hand, simple bar code labels are much cheaper and can be generated faster.